The invention relates to a coupling according to the definition of the species of claim 1 and an apparatus with a multiplicity of such couplings.
The recording carriers may be, for example, individual sheets or also envelopes and they are designated subsequently only as sheets for the sake of simplicity. Customarily, a separating arrangement has at least a separating roller engaging with frictional contact at the stack of sheets and, as is well known, serves also for feeding the sheets right into the pulling in gap of the platen. An arrangement containing such couplings is intended for being placed onto an office machine, for example, a typewriter or an automatic writing device such as a printer, and is driven by the drive of the platen. The platen at the same time is coupled with a reversible drive, whereby the direction of rotation of the platen is designated as a forward rotational direction in the pulling-in direction of the sheet and the opposite rotational direction as a reverse rotational direction. The rotational directions mentioned in the case of the explanation of the coupling correspond to those of the platen.
A coupling of the type mentioned has been known from the German Patent No. 29 50 707. As connecting elements for coupling, this known coupling has a stop lever between the driver and the output shaft, a control disc, a driver peg disposed on the control disc, a driver disc and an idler wheel connected with it. If one takes into consideration that the idler wheel also consists of a number of individual parts, then the expenditure of connecting elements is relatively great. Despite such an expenditure, this known coupling is not suitable for the printing of graphic presentations, in the case of which the platen has to be turned forward and backward for the purpose of the process of recording, because the coupling would engage anew, for example, after a turn in the backward direction.
The apparatus known from the publication cited furthermore has the disadvantage that a three time reversal of the platen is necessary in order to drive the separating arrangement after the third reversal during a return run of the platen. As a result of such a function, the fed in sheet may not be pulled in by the platen during the feeding in process so that it is held up at the input gap of the platen and is arched as a result of the forward movement of the separating apparatus. Only by a further reversing of the platen into the forward rotational direction will the sheet be transported by the platen.